Yamaha DX7 Faulty/Defectuous powerplug/internal transformer

[Operatron]

I brought a near mint condition Yamaha DX7 about 3/4 days ago and I been playing/experimenting/learning FM synthesis ever since but yesterday I plugged the synth and turned on while I was reading a FM tutorial and after about 5 minutes into the tutorial I noticed a slightly burning smell so I stopped reading and I started sniffing for the smell source and it seems that the back rigth side of the synth was way too hot and by now it smelled like toxic like overheated plastic so I try to switch off the synth but it didn't ,so I go running and just unplug the synth from the wall , so then after a few minutes (another five perhaps) I open the doors and windows because the smell was a bit too concentrated ...., then I open the synth to see wtf happened or at least get a clue of why ,and the smell/heat seems to come from the back rigth of my DX , the left was as good as new , I checked the memory/battery a day before that happened and it said 2.9 wich is good so I'm quite sure is not the battery ,though I remember noticing quite hot to the touch even back then but I asumed that it was natural from a synth that size and weight (having owned an alesis micron the manual says that is ok for the synth to get hot...and the DX is nearly 4 times the size of a micron)so I tough it was good .......
I plugged on and quickly went thru the presets and they seem to work but it won't switch off by the back so I have to unplug it from the main and by now I'm cosiderating a tech ........... :/
So anyone have any ideas/theories of what migth of happened ?

PS:I can upload pics if necessary allthought there's no apparent/obvious/visible reason from my untrained eyes .

Thanks




Sebastian

[Synthaholic]

Actually, if you could upload pics (with the synth opened up) it would be helpful. Especially if you can point out the location where the heat/smell was coming from.

AFAIK the DX7 isn't known for getting hot, so you likely have an issue with the power supply.

Sounds like your unit has a faulty power switch as well.

Is it a mkI DX7 or a mkII?

[Operatron]

Actually, if you could upload pics (with the synth opened up) it would be helpful. Especially if you can point out the location where the heat/smell was coming from.

AFAIK the DX7 isn't known for getting hot, so you likely have an issue with the power supply.

Sounds like your unit has a faulty power switch as well.

Is it a mkI DX7 or a mkII?

It's an MKI

[Operatron]

*Hey there again , here's a wee update after reading/researching in the net for a while : the burning smell migth come from the nearly 20 year old fuses in the DX7 , I once again opened my DX and with the help of a magnifier I carefully looked thru the litlle fuses and I found that fuses 1 and 2 of the 4 are slightly shiny and melted on the centre resulting in a acumulation of melted metal/residue ,yet the litlle metal strings still in one piece , fuse 1 [partially melted ] migth be interfering with the on-off switch circuit as it doesn't seeem to be able to turn off when plugged in ,and since originally left on for about 5 ++ mins resulting in a very strong burning smell , I'm still unable to explain the mild heat from the device a couple of days ago..... , allthought I think it was [or not]a litlle exaggeration from my side ;P ........
Well I'm still unable to get the synth inspected/fixed [and hopefully its just the dx7's 20 y o fuses] since I'm away for a couple of weeks .......




Many thanks



Sebs

[placemat]

I've had exactly the same issue with my MK1 Dx7. Has anyone worked out what the problem was as this thread is still wide open? I left my DX for a couple of days, then opened the hood to have a look at those pesky fuses. Some indeed did look a bit 'cloudy' and there was also a clump of furry dust around the two wires from the power switch. I removed the dust, then switched it on. It didn't continue smelling, I just had the residue smell from a couple of days ago. I plugged in my headphones and all seemed to be ok. It would also now switch off which it didn't before. I'm still concerned to what it could have been. If anyone can throw some light on the issue, I'd be grateful.

[meatballfulton]

That "clump of furry dust" was probably shorting the switch, preventing turning the unit off. I've seen lots of interesting circuit failures caused by nothing more than buildup of crud on contacts...cleaning the contacts made the problems go away.

[Sonus]

You better fix it before the RFI capacitor burns out...



http://www.yamahaforums.co.uk/forum/vie ... php?t=5994

[placemat]

You better fix it before the RFI capacitor burns out...

Wow is that black where the board has been scorched?! I'll take another look to be sure. It mentions to buy an X2 capacitor. I'm no electrician but I can soldier as long as I have the correct parts! I'll check for any scorch marks around that component before I think of switching it back on. Thank you for the link too. Very interesting.

[placemat]

Below are a couple of photos of the fuse board. There doesn't seem to be any signs of burning or scorching. It seems ok at the moment (fingers crossed). I'm hoping that it was just the build up of dust around the two switch wires. I'll be keeping a beady eye and a keen nose on it!

[cso5]

Just check the capacitor next to the white plug with the purple and orange wires. The cap is split you should change it.

[placemat]

Just check the capacitor next to the white plug with the purple and orange wires. The cap is split you should change it.

Ah, well from the look of it in the picture, it is split. Do you or anyone know what the correct part is called & where to get one from? Many thanks for the advice by the way.

[blueknob]

yey result! when I first started reading the opening message I was thinking to myself.. yeh I've had that, the smoke poured into my room, it was quite impressive, I couldn't see across the room, no bangs or sparks just a huge amount of brown smoke. Indeed was that mains capacitor, the one that might be marked C10 (not the circular blue one) butt up to the white connector.
These usually are made by RIFA I think from Germany too. They value will be on the circuit diagram, it will be something like 100nF 250V X or Y rated (which is the important part), these chaps are now falling over. You could remove the debris (desolder) and the DX7 should run fine, but without the EMC certification, not a problem. But know, this is on the mains side and has high voltage on, it can be very dangeous to try things if unsure.

[Werecow]

The cap is shown as 0.022μF, 250V on the schematic for both US and UK models. The 250V part leaves almost no safety margin if you have 230V mains, so replace with a higher voltage part in that case.

A safety-certified X or Y class cap isn't necessary in this application, but if it does fail, you'll still be able to turn off the synth with the switch (X and Y class won't fail shorted), and the cap won't turn into a flamethrower.

[placemat]

Thank you Werecow for the info. I will try and find a replacement cap. I'm in the uk so I would need a higher voltage part. I'll find an electrician/engineer who might be willing to do the job for me.
Thanks again!

[placemat]

The cap is shown as 0.022μF, 250V on the schematic for both US and UK models. The 250V part leaves almost no safety margin if you have 230V mains, so replace with a higher voltage part in that case.

A safety-certified X or Y class cap isn't necessary in this application, but if it does fail, you'll still be able to turn off the synth with the switch (X and Y class won't fail shorted), and the cap won't turn into a flamethrower.

Would this be the correct part? If so I'll order it and de soldier the old one then re soldier this...
https://www.amazon.co.uk/Capacitor-0-02 ... B00AZJFT66

There is also this one...

http://www.ebay.co.uk/itm/B32560-J3223- ... 2110654192

Many thanks!